1. Field of the Invention
The present invention relates in general to VHS video cassette service equipment, and in particular to VHS video service jigs or cassettes that simulate selected functions of a genuine cassette in ways helpful to a VCR service technician.
2. Description of Related Art
More than thirty-five million video cassette recorders, or VCRs as they are often called, are in use in the United States, and tens of millions of other VCRs are in use in other countries throughout the world. Almost all of these units will require some sort of maintenance or service, if used for a sufficiently long time.
Videotape recording formats used in the United States include the VHS format, the Beta format and the 8 millimeter format. The VHS format is the most popular format, and VCRs for the VHS format are made by the greatest number of manufacturers. The dimensions and operation of both the Beta format and 8 millimeter format video cassette recorders are substantially different. The service cassettes of the present invention is focused upon VHS format VCRs and thus the other formats will not be discussed.
Japanese companies that actually manufacture VCRs for VHS format include NEC, Hitachi, Matsushita, Mitsubishi, Sanyo, Sony and others. Korean companies which manufacture VCRs for the VHS format include Samsung and others. Many VCRs made by these Japanese companies are sold under private labels of still other companies. The VCRs for which play the VHS format all accept a standard size tape cassette familiar to all individuals who have used or service a VHS video cassette recorder. Hundreds of millions of these cassettes have been produced and sold, many as blank tapes for home or professional recording purposes, and still many others for use with prerecorded video material from commercial sources such as Hollywood film studios and music videos. VHS tape cassettes have gained wide acceptance since they provide a convenient, rugged, tamper-resistant protective casing for the spool of 0.5 inch (1.3 cm) wide magnetic tape wound on a pair of supply and takeup reels. The magnetic tape is normally provided with a clear leader and a clear trailer, each of which are several inches in length. These clear leader and trailer portions have the same general dimensions and flexibility as the other part of the tape, but lack the magnetic recording material, such as a ferrous oxide coating, normally found on the rest of the tape. The clear leaders and trailers are substantially transparent and therefore allow light to shine therethrough, while the other portions of the tape containing magnetic recording material are substantially opaque and block a beam of light. The presence or absence of the transparent leader or trailer is detected by one of two photodiodes spaced apart from one another and located next to the tape cassette handling mechanism within a VCR unit, and are used to tell the automatic tape handling equipment of the VCR when to start and stop in the various modes of operation.
All of the VCRs produced by the various manufacturers of units for VHS format will accept the standard size VHS cassette, even though the internal mechanisms within the VCR units which interact with the cassette are designed somewhat differently from manufacturer to manufacturer. There are two principal systems which interact with the standard VHS cassette, the first being in the tape loading system which transports the tape cassette into and out of the VCR, and second being the tape handling system. To load a tape cassette, the tape loading system normally transports the tape cassette horizontally in a first direction into the VCR. and then vertically downwardly to drop the tape cassette into its operating position within the VCR. To eject a tape cassette for the VCR unit, this same system raises the tape upwardly from its operating position, and then transports it horizontally in a second direction opposite the first direction.
The tape handling system, interacts with the videotape in order to perform the usual set of functions provided on most VCR units. These functions include fast forward, fast reverse, play, record, pause and stop. Several different fairly complex movements are carried out by the tape handling system in order to accomplish the foregoing functions. In particular, a portion of the tape is extracted by a pair of movable guide roller assemblies from the tape cassette when in its normal operating position. The extracted tape is wrapped in an extended arc about the circular recording drum in the play and record modes, and retracted from that position in the normal rewind sequence executed as part of the stop mode.
In order to perform a routine maintenance or other service upon the cassette transport system or the tape handling system of a VCR unit, the cover of the VCR is removed to expose these components. Then a cassette tape is inserted into the tape transport system and lowered into position, while the technician servicing the unit watches the operation of the internal components of the cassette transport system and the tape handling system. In this manner, the technician is at times able to observe or deduce the point in the operating cycle of either of these systems where some abnormality is occurring. Armed with that information, the technician can sometimes ascertain the cause or origin of the malfunction with the unit. Thereafter, the tape cassette is removed and the necessary adjustments are made. A tape cassette is once again inserted and the accuracy of the adjustments and replaced parts are then reviewed by putting the VCR unit through its paces to see whether it performs all of its functions within the tolerances set by the manufacturer's specifications.
The presence of the tape cassette within the tape transport system and/or the tape handling system obscures the technician's view of the movements and operation of a number of key components of the two systems. Thus, the technician is not always able to determine at what portion of a given cycle the conventional tape transport system or tape handling system is malfunctioning, but instead, must guess based upon the evidence before him. Also, in almost all of the VCR units, there are a number of mechanical and/or electronic alignments or adjustments which cannot be made when the tape cassette is in place in the transport system or in the tape handling system. This represents a shortcoming in the ability to efficiently, easily and reliably service VCRs in the home or at the service technician's shop.
Crestwood Products, Inc., of Des Plaines, Ill. recognized this shortcoming and offers to the VCR service trade a service cassette intended to help overcome these problems. This Crestwood Products tool is also called a VHS view-through diagnostic tool or jig that allows the operation of a VCR unit as if there were a regular cassette tape in it. In other words, the view-through tool does not include a magnetic cassette tape but instead is a plastic-injection molded frame reportedly having the same length and width as a regular VHS cassette. The unit is made of transparent plastic material, which allows the technician to see through portions of the frame and thereby determine what is going on underneath the area where a normal cassette would be positioned by the tape cassette loading system. The view-through tool includes a central member that is parallel to the left and right end walls, and is attached to the front and rear walls of the unit. The two halves enclosed by the end walls and central wall is open, except for plastic plates which contact the "cassette present" switches at the bottom of travel in the tape transport system.
In spite of its usefulness, the Crestwood service jig still has a number of drawbacks. The rear wall and central member of its frame impedes access by the technician to some components of the tape handling mechanism. Further, even though the Crestwood service jig is made of transparent plastic material, it still obscures the ability of the technician to observe components lying adjacent to it, on account of the reflective properties of the plastic and the fact that the edges do not appear to be transparent. Further, these rear wall portions and central wall portions block access to the components, as do the plates which actuate the contact switches that extend across the entire length of the bottom front of the service jig. Also, the Crestwood service cassette cannot be used with a number of newer VCR models, on account of the different mechanism used to open the tape cassette access door. Specifically, some newer VCR models made by Matsushita feature a compound-motion lever or actuator mechanism to flip open the access door of a conventional VHS tape cassette as the cassette transport system advances and lowers the VHS cassette into its operating position within the unit. Such door opening mechanisms normally require that the cassette and its access door go through a predetermined pattern of movement and the door provide a predetermined range of resistance which signifies that the door has been successfully contacted and is being flipped open. The Crestwood service jig has no provision for simulating this door opening function, and accordingly cannot be used to service these later Matsushita VHS models. Further, the lip in the front center of the Crestwood jig does not successfully operate all models of the top mechanical "cassette inserted" switch found in such VCR models as the Sharp and the Samsung VHS units.
In light of the foregoing limitations of the Crestwood Products service jig and in order to advance the state of the art for servicing VHS VCRs, it is an object of the present invention to provide a service jig which is easy to use and works safely with virtually all makes and models of VHS VCRs, including the newer models made by Matsushita, and allows such VCRs to be placed in any normal mode of operation. Newer models made by Matsushita are sold under the labels of other companies including Panasonic, Quasar, GE, RCA, Sylvania, Magnavox, Philco, Philips (USA) and Technics.
It is a related object of the present invention to provide a service jig with a entirely open tape loop area, which still simulates the placement of a normal video cassette into the VCR.
It is yet another object of the present invention to provide a service jig which safely operates the top "cassette inserted" switch of all of the VCR units which have them.
It is a further object of the present invention to provide a service jig with a compact, reliable mechanism that simulates the operation of a front cover of a tape cassette flipping over upon being advanced and lowered into operating position within a VCR unit.